Flashcards in Common Cestode Infections Deck (31)
What are some common cestode worm infections? Give latin and common names.
- Taenia saginata; beef tapeworm
- Taenia solium; pig tapeworm
- Echinococcus granulosus; hydatid tapeworm
- Echinococcus multilocularis; small fox tapeworm
What are some key facts for the Taenia spp. genus of cestodes? (Hosts? Infection? Home?)
- Taenia solium (pig tapeworm) and Taenia saginata (beef tapeworm) are segmented tapeworms; cestodes
- Humans are the only DEFINITIVE hosts for T. saginata, T.solium and T.asiatica.
- Infection (of humans) through raw or undercooked meat
- Adult worms attach to the small intestine via their scolex, growing to 5-7 metres (but can reach 25 metres); small intestine gives enough space for growth.
What is meant by a definitive host?
The host in which parasites become sexually mature; F, M or hermaphrodite.
How does Taenia morphology differ between T. saginata and T.solium? What is its significance?
- The front section of Taenia is the 'scolex'
- Scolex of T. saginata has four large suckers
- However, T. solium has four suckeres AND a rostellum (hooks); two rows of large and small hooks, 13 hooks of each size.
- Thus T. solium's rostellum is an important diagnostic feature.
How does T. asiatica's scolex compare to T. saginata (beef tapeworm) and T. solium?
A hybrid of the two; T. asiatica (Asian tapeworm) possesses rudimentary hooklets (rostellum) in a wart-like formation.
What are proglottids, and where are they most mature?
- Single segments of a cestode worm
- Initial proglottids behind scolex are immature, but are progressively more mature and thicker the further from the scolex
- Cestodes = hermaphrodites; each proglottid has both ovaries and testes; the proglottid detaching when mature (filled with eggs), crawling out of the anus and in the faeces.
Describe the lifecycle for Taenia spp.
1) Eggs or gravid (carrying eggs) proglottids passed in faeces, into environment
2) Cattle (T .sagninata) and pigs (T. solium) [intermediate hosts] become infected by ingesting vegetation contaminated by eggs/gravid proglottids
3) Oncospheres hatch, penetrating intestinal wall, circulate to striated muscles, where they develop into cysticerci.
4) Humans infected by ingesting raw/undercooked infected meat. Cysticercus develops over 2 months into an adult tapeworm in the intestine, can survive for years.
5) Adult tapeworm attaches to small intestine by their scolex (counteracts peristalsis)
6) Reside in the small intestine.
Adults produce proglottids, they mature, become gravid, detach, migrate to the anus/passed in stool. One proglottid can produce 50,000 (T. solium) to 100,000 (T. saginata) eggs; approximates 6 proglottids are passed in the stool each day.
What is the pathology of Taenia saginata (and mostly T. solium) infection?
- Only few symptoms, associated w/presence of adult worms in intestine
- Obstruction, diarrhoea, hunger pains, weight loss or appendicitis have been reported (rare)
- Most common complaint: discomfort/embarrassment caused by proglottids crawling from the anus.
What is the difference between Taeniasis infection by ingesting cysticerci in raw meat and ingesting egg/gravid proglottids of Taenia solium?
- Taeniasis; infection from ingesting raw/undercooked meat containing cysticerci (normal life cycle), symptoms moderate.
- Cysticercosis; humans accidentally ingesting eggs/gravid proglottids of Taenia solium (human become intermediate host).
>>> Pathology much more severe, can be fatal.
What is the life cycle for Taenia solium, resulting in cysticercosis?
- Pigs/humans infected by ingesting eggs/gravid proglottids
- Human infection by ingestion of food contaminated w/faeces, or by autoinfection (faecal-oral)
- Once eggs ingested, oncospheres hatch in intestine
- Eggs invade intestinal wall, migrate to striated muscles, as well as the brain, liver and other tissues, developing into cysticerci.
- Cysts localised in the brain can cause neurocysticercosis.
- Parasite life cycle is completed when the human ingests undercooked/raw pork containing cysticerci.
- These attach to the small intestine by scolex, adult tapeworms develop, produce proglottids, reside in small intestine etc.
What is the pathology of cysticercosis?
- T. solium eggs activated by GI secretions, release infective larvae; oncospheres
- Oncospheres cross intestinal wall, end up anywhere in the body, undergoing further maturation to cysticerci (1-2 months)
- Mainly found in CNS and eyes (affinity to CNS tissue), more rarely in subcutaneous tissue and muscle.
- 2mm - 2 cm in size
- SC cysts do not cause any pathology
- However, CNS or ocular disease can cause serious problems: seizures, intracranial hypertension.
What is the treatment for Taeniasis or cysticercosis? What are these agents called?
> Both unlicensed in the UK (too rare)
What does treatment of taeniasis with PZQ (praziquantel) result in?
- Flatworm (tapeworm; Taenia sagnitata/solium) loses its ability to resist digestion
- Degraded in gut (rarely passed whole)
What can PZQ also be used to treat aside from Taeniasis?
- Schistosoma (tropical disease)
What is Niclosamide mode of action in treating Taeniasis? Why is praziquantel (PZQ) preferred?
- Inhibits glucose uptake and oxidative phosphorylation
- Not effective against pinworms (Enterobius vermicularis) or roundworms (Ascaris lumbricoides); ONLY for flatworms
- Cheap and effective but numerous side effects; thus use PZQ first.
What is a zoonotic infection?
- When a pathogen which is usually found in animals occasionally infects humans
- E.g Plasmodium knowlesi (monkeys), avian flu.
Why are zoonotic infections important? (Name 3 reasons)
- Animal reservoir; more difficult to eradicate
- Pathology often more severe than human parasites; more symptoms 'in wrong host' = big immune reactions, big inflammation
- Can be transmitted by pets or livestock
What species of Echinococcus can be pathogenic for humans? What are their common names? (2)
- Echinococcus granulosus; cystic echinococcosis
- Echinococcus multilocularis; alveolar echinococcosis
What is the lifecycle for Echinococcus?
1) Adult Echinococcus granulosus (3 to 6mm long) resides in the small bowel of definitive hosts
2) Gravid proglottids release eggs in faeces, ingestion by intermediate host.
3) Egg hatches in small intestine, releases oncosphere (larvae), penetrates intestinal wall and migrates through circulatory system into various organs; especially liver and lungs.
4) In these organs, the oncosphere develops into a hydatid cyst. Cyst enlarges gradually, producing protoscolices and daughter cysts that fill the cyst.
5) Definitive host infective by ingesting cyst-containing organs of intermediate host. Protoscolices evaginate.
6) Attaching to small intestine (scolex; cestodes), developing into adult stages in 32 to 80 days.
What are the definitive hosts for Echinococcus, and the intermediate ones?
- Definitive; dogs, other canidae e.g. wolf/fox/dingo
- Intermediate; sheeps, goats, swine
What are the symptoms for Echinococcus granulosus (cystic) infection?
- May be asymptomatic for years
- Cysts slow growing
- Symptoms depend on: size (and location), causing non-specific symptoms such as cough, abdominal pain, discomfort
What can result from rupture of Echinococcus granulosus cysts? Caveat?
- E.g. in surgery; can cause allergic reactions, and death by anaphylactic shock
- Flood organs with parasitic bacteria, IgE sensitisation, massive histamine release etc.
- BUT, surgery is only cure.
What are the symptoms of alveolar echinococcosis? What is it caused by?
- Caused by Echinococcus multilocularis
- Asymptomatic incubation of 5-15 years
- Larvae do not fully mature to cysts in humans, but form vesicles which invade and destroy neighbouring tissues, invading as premature cysts (want to be in proper intermediate host; sheep, but signals missing of where to go)
- Growth similar to metastatic cancer
- Mortality is high (50-75%)
- Clinical signs: weight loss, abdominal pain, general malaise, signs of hepatic failure.
How is Echinococcosis transmitted?
- Dogs infected by eating e.g. liver of infected sheep
- Tapeworm eggs then found in dog's stool (definitive host)
- Humans infected by faecal-oral transmission, leading to ingestion of eggs, e.g. by intimate handling of pet (fur may contain eggs) or also by contaminated soil or vegetables.
- Echinococcus granulosus eggs can survive snow and freezing conditions.
What is the pathology of Echinococcus infection?
- Dependent on size, quantity, location of cysts (e.g. neurological symptoms)
- Cysts can grow to large size without causing symptoms; but small cysts in wrong location can cause severe symptoms e.g. compression of vitals (nerve/brain/vasculature)
- Alveolar echinococcus similar to slow growing metastatic tumour, spreading either to organ adjacent liver (spleen) or distant locations (lungs, brain) following dissemination (spreading) of the parasite via blood and lymphatics.
How is Echinococcosis diagnosed?
- Ultrasound; imaging technique of choice, CT/MRI used to confirm diagnosis if cystic or alveolar echinococcosis.
- Serological tests (antibody detection) may be used to confirm diagnosis; but cross-reactivity w/different parasites, hence conformational technique.
- BUT, neither technique can diagnose a recent primary infection; no cysts/antibodies yet
- NO egg detection in faeces (of humans)
How is echinococcosis treated?
- Mebendazole (Ovex); well tolerated, efficacy against cystic echinococcosis.
- PZQ (Praziquantel); given concomitantly with Mebendazole.
CIs: large cysts with risk of rupture, inactive or calcified cysts, early pregnancy.
What are the four options for treatment of cystic echinococcosis?
- Percutaneous treatment of hydatid cysts w/PAIR minimal invasive technique (Puncture, Aspiration, Injection, Re-aspiration)
- Anti-infective drug treatment (Mebendazole, PZQ)
- 'Watch and wait' - pregnancy
What does the PAIR minimal invasive technique entail,a and what is it used to treat?
- Locating cyst and sucking out contents
- Injecting drug to kill parasite
- And then re-aspire